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                MySQL---常见函数
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        <h1 id="字符函数"><a href="#字符函数" class="headerlink" title="字符函数"></a>字符函数</h1><table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">CONCAT()</td>
<td style="text-align:center">字符连接</td>
</tr>
<tr>
<td style="text-align:center">CANCAT_WS(“分隔符”,”value”,”value”,..)</td>
<td style="text-align:center">用指定分隔符进行字符连接</td>
</tr>
<tr>
<td style="text-align:center">FORMAT()</td>
<td style="text-align:center">数字格式化</td>
</tr>
<tr>
<td style="text-align:center">LOWER()</td>
<td style="text-align:center">转换成小写</td>
</tr>
<tr>
<td style="text-align:center">UPPER()</td>
<td style="text-align:center">转换成大写</td>
</tr>
<tr>
<td style="text-align:center">LEFT()</td>
<td style="text-align:center">从左侧开始截取</td>
</tr>
<tr>
<td style="text-align:center">RIGHT()</td>
<td style="text-align:center">从右侧开始截取</td>
</tr>
</tbody>
</table>
<a id="more"></a>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div></pre></td><td class="code"><pre><div class="line">// 使用CONCAT拼接字符串</div><div class="line">mysql&gt; SELECT CONCAT(&quot;A&quot;,&quot;B&quot;,&quot;C&quot;);</div><div class="line">+---------------------+</div><div class="line">| CONCAT(&quot;A&quot;,&quot;B&quot;,&quot;C&quot;) |</div><div class="line">+---------------------+</div><div class="line">| ABC                 |</div><div class="line">+---------------------+</div><div class="line"></div><div class="line">// CONCAT_WS用指定分隔符拼接字符串</div><div class="line">mysql&gt; SELECT CONCAT_WS(&quot;-&quot;,&quot;A&quot;,&quot;B&quot;,&apos;C&apos;);</div><div class="line">+----------------------------+</div><div class="line">| CONCAT_WS(&quot;-&quot;,&quot;A&quot;,&quot;B&quot;,&apos;C&apos;) |</div><div class="line">+----------------------------+</div><div class="line">| A-B-C                      |</div><div class="line">+----------------------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT CONCAT_WS(&quot;-&quot;,id,username) FROM user ;</div><div class="line">+----------------------------+</div><div class="line">| CONCAT_WS(&quot;-&quot;,id,username) |</div><div class="line">+----------------------------+</div><div class="line">| 1-TOM                      |</div><div class="line">| 2-JERRY                    |</div><div class="line">| 3-ALICE                    |</div><div class="line">+----------------------------+</div><div class="line"></div><div class="line">// 格式化数字函数</div><div class="line">mysql&gt; SELECT FORMAT(100.111,2);</div><div class="line">+-------------------+</div><div class="line">| FORMAT(100.111,2) |</div><div class="line">+-------------------+</div><div class="line">| 100.11            |</div><div class="line">+-------------------+</div><div class="line"></div><div class="line">// 小写</div><div class="line">mysql&gt; SELECT LOWER(&quot;MYSQL&quot;);</div><div class="line">+----------------+</div><div class="line">| LOWER(&quot;MYSQL&quot;) |</div><div class="line">+----------------+</div><div class="line">| mysql          |</div><div class="line">+----------------+</div><div class="line"></div><div class="line">// 大写</div><div class="line">mysql&gt; SELECT UPPER(&quot;mysql&quot;);</div><div class="line">+----------------+</div><div class="line">| UPPER(&quot;mysql&quot;) |</div><div class="line">+----------------+</div><div class="line">| MYSQL          |</div><div class="line">+----------------+</div><div class="line"></div><div class="line">// 从左侧截取</div><div class="line">mysql&gt; SELECT LEFT(&quot;MYSQL&quot;,2);</div><div class="line">+-----------------+</div><div class="line">| LEFT(&quot;MYSQL&quot;,2) |</div><div class="line">+-----------------+</div><div class="line">| MY              |</div><div class="line">+-----------------+</div><div class="line"></div><div class="line">// 从右侧截取</div><div class="line">mysql&gt; SELECT RIGHT(&quot;MYSQL&quot;,2);</div><div class="line">+------------------+</div><div class="line">| RIGHT(&quot;MYSQL&quot;,2) |</div><div class="line">+------------------+</div><div class="line">| QL               |</div><div class="line">+------------------+</div></pre></td></tr></table></figure>
<table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">LENGTH()</td>
<td style="text-align:center">获取字符串长度</td>
</tr>
<tr>
<td style="text-align:center">LTRIM()</td>
<td style="text-align:center">删除签到空格</td>
</tr>
<tr>
<td style="text-align:center">RTRIM()</td>
<td style="text-align:center">删除后续空格</td>
</tr>
<tr>
<td style="text-align:center">TRIM()</td>
<td style="text-align:center">删除和替换前导和后续空格(完整格式：TRIM([{BOTH / LEADING /TRAILING} [remstr] FROM] str))</td>
</tr>
<tr>
<td style="text-align:center">SUBSTRING()</td>
<td style="text-align:center">字符串截取</td>
</tr>
<tr>
<td style="text-align:center">[NOT] LIKE</td>
<td style="text-align:center">字符串匹配(%任意多个字符，_单个字符)</td>
</tr>
<tr>
<td style="text-align:center">REPLACE()</td>
<td style="text-align:center">字符串替换</td>
</tr>
</tbody>
</table>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div></pre></td><td class="code"><pre><div class="line">// 获得字符串长度</div><div class="line">mysql&gt; SELECT LENGTH (&quot;MY SQL&quot;);</div><div class="line">+-------------------+</div><div class="line">| LENGTH (&quot;MY SQL&quot;) |</div><div class="line">+-------------------+</div><div class="line">|                 6 |</div><div class="line">+-------------------+</div><div class="line"></div><div class="line">// 清除左边的空格</div><div class="line">mysql&gt; SELECT LTRIM(&quot;    MYSQL   &quot;);</div><div class="line">+-----------------------+</div><div class="line">| LTRIM(&quot;    MYSQL   &quot;) |</div><div class="line">+-----------------------+</div><div class="line">| MYSQL                 |</div><div class="line">+-----------------------+</div><div class="line"></div><div class="line">// 计算清除过后的长度</div><div class="line">mysql&gt; SELECT LENGTH(LTRIM(&quot;   MY SQL &quot;));</div><div class="line">+-----------------------------+</div><div class="line">| LENGTH(LTRIM(&quot;   MY SQL &quot;)) |</div><div class="line">+-----------------------------+</div><div class="line">|                           7 |</div><div class="line">+-----------------------------+</div><div class="line"></div><div class="line">// 清除右侧的空格</div><div class="line">mysql&gt; SELECT LENGTH(RTRIM(&quot;   MY SQL &quot;));</div><div class="line">+-----------------------------+</div><div class="line">| LENGTH(RTRIM(&quot;   MY SQL &quot;)) |</div><div class="line">+-----------------------------+</div><div class="line">|                           9 |</div><div class="line">+-----------------------------+</div><div class="line"></div><div class="line">// 清除左侧和右侧的空格</div><div class="line">mysql&gt; SELECT LENGTH(TRIM(&quot;   MY SQL &quot;));</div><div class="line">+----------------------------+</div><div class="line">| LENGTH(TRIM(&quot;   MY SQL &quot;)) |</div><div class="line">+----------------------------+</div><div class="line">|                          6 |</div><div class="line">+----------------------------+</div><div class="line"></div><div class="line">// trim还可以用来替换指定字符</div><div class="line">mysql&gt; SELECT TRIM(BOTH &quot;?&quot; FROM &quot;?MY?SQL?&quot;);</div><div class="line">+--------------------------------+</div><div class="line">| TRIM(BOTH &quot;?&quot; FROM &quot;?MY?SQL?&quot;) |</div><div class="line">+--------------------------------+</div><div class="line">| MY?SQL                         |</div><div class="line">+--------------------------------+</div><div class="line"></div><div class="line">// 求字串，序号从1开始</div><div class="line">mysql&gt; SELECT SUBSTRING(&quot;MYSQL&quot;,1,2);</div><div class="line">+------------------------+</div><div class="line">| SUBSTRING(&quot;MYSQL&quot;,1,2) |</div><div class="line">+------------------------+</div><div class="line">| MY                     |</div><div class="line">+------------------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT SUBSTRING(&quot;MYSQL&quot;,-3);</div><div class="line">+-----------------------+</div><div class="line">| SUBSTRING(&quot;MYSQL&quot;,-3) |</div><div class="line">+-----------------------+</div><div class="line">| SQL                   |</div><div class="line">+-----------------------+</div><div class="line"></div><div class="line">// 模糊查找，% 表示任意多个字符</div><div class="line">mysql&gt; SELECT * FROM user WHERE username LIKE &quot;%O%&quot;；</div><div class="line">+----+----------+------+</div><div class="line">| id | username | pid  |</div><div class="line">+----+----------+------+</div><div class="line">|  1 | TOM      |    1 |</div><div class="line">+----+----------+------+</div><div class="line"></div><div class="line">// \表示转义字符</div><div class="line">mysql&gt; SELECT * FROM user WHERE username LIKE &quot;%\%%&quot;;</div><div class="line">+----+-----------+------+</div><div class="line">| id | username  | pid  |</div><div class="line">+----+-----------+------+</div><div class="line">|  4 | TOM%JERRY |    1 |</div><div class="line">+----+-----------+------+</div><div class="line"></div><div class="line">// 使用escape自定义转移字符</div><div class="line">mysql&gt; SELECT * FROM user WHERE username LIKE &quot;%:%%&quot; ESCAPE &quot;:&quot;;</div><div class="line">+----+-----------+------+</div><div class="line">| id | username  | pid  |</div><div class="line">+----+-----------+------+</div><div class="line">|  4 | TOM%JERRY |    1 |</div><div class="line">+----+-----------+------+</div></pre></td></tr></table></figure>
<h1 id="数值运算符函数"><a href="#数值运算符函数" class="headerlink" title="数值运算符函数"></a>数值运算符函数</h1><table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">DIV</td>
<td style="text-align:center">整数除法</td>
</tr>
<tr>
<td style="text-align:center">MOD</td>
<td style="text-align:center">取余数</td>
</tr>
<tr>
<td style="text-align:center">CEIL()</td>
<td style="text-align:center">进一取整</td>
</tr>
<tr>
<td style="text-align:center">FLOOR()</td>
<td style="text-align:center">舍一取证</td>
</tr>
<tr>
<td style="text-align:center">POWER(a,b)</td>
<td style="text-align:center">幂运算(a的b次方)</td>
</tr>
<tr>
<td style="text-align:center">ROUND(num[,length])</td>
<td style="text-align:center">四舍五入，指定位数的四舍五入</td>
</tr>
<tr>
<td style="text-align:center">TRUNCATE()</td>
<td style="text-align:center">数字截取（不进行四舍五入）</td>
</tr>
<tr>
<td style="text-align:center">[NOT]BETWEEN…AND…</td>
<td style="text-align:center">[不]在范围内</td>
</tr>
<tr>
<td style="text-align:center">[NOT]IN()</td>
<td style="text-align:center">[不]在列出值范围内</td>
</tr>
<tr>
<td style="text-align:center">IS [NOT] NULL</td>
<td style="text-align:center">判断是否为空</td>
</tr>
</tbody>
</table>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div></pre></td><td class="code"><pre><div class="line">// 进一</div><div class="line">mysql&gt; SELECT CEIL(3.01);</div><div class="line">+------------+</div><div class="line">| CEIL(3.01) |</div><div class="line">+------------+</div><div class="line">|          4 |</div><div class="line">+------------+</div><div class="line"></div><div class="line">// 舍一</div><div class="line">mysql&gt; SELECT FLOOR(3.99);</div><div class="line">+-------------+</div><div class="line">| FLOOR(3.99) |</div><div class="line">+-------------+</div><div class="line">|           3 |</div><div class="line">+-------------+</div><div class="line"></div><div class="line">// 指定位数的四舍五入</div><div class="line">mysql&gt; SELECT ROUND(10.1234,3);</div><div class="line">+------------------+</div><div class="line">| ROUND(10.1234,3) |</div><div class="line">+------------------+</div><div class="line">|           10.123 |</div><div class="line">+------------------+</div><div class="line"></div><div class="line">// 数字的截取</div><div class="line">mysql&gt; SELECT TRUNCATE(1.23456,2);</div><div class="line">+---------------------+</div><div class="line">| TRUNCATE(1.23456,2) |</div><div class="line">+---------------------+</div><div class="line">|                1.23 |</div><div class="line">+---------------------+</div><div class="line"></div><div class="line">// between .. and...</div><div class="line">mysql&gt; SELECT 10 BETWEEN 1 AND 100 ;</div><div class="line">+----------------------+</div><div class="line">| 10 BETWEEN 1 AND 100 |</div><div class="line">+----------------------+</div><div class="line">|                    1 |</div><div class="line">+----------------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT 10 IN(10,20,30);</div><div class="line">+-----------------+</div><div class="line">| 10 IN(10,20,30) |</div><div class="line">+-----------------+</div><div class="line">|               1 |</div><div class="line">+-----------------+</div><div class="line">1 row in set (0.04 sec)</div></pre></td></tr></table></figure>
<h1 id="日期和时间函数"><a href="#日期和时间函数" class="headerlink" title="日期和时间函数"></a>日期和时间函数</h1><table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">NOW()</td>
<td style="text-align:center">当前日期和时间(2017-07-10 11:16:20)</td>
</tr>
<tr>
<td style="text-align:center">CURDATE()</td>
<td style="text-align:center">当前日期(2017-07-10)</td>
</tr>
<tr>
<td style="text-align:center">SURTIME()</td>
<td style="text-align:center">当前时间(11:16:38 )</td>
</tr>
<tr>
<td style="text-align:center">DATE_ADD(date,INTERVAL expr type)</td>
<td style="text-align:center">日期变化(YEAR/MONTH/WEEK/DAY/HOUR/MINUTE/SECOND)</td>
</tr>
<tr>
<td style="text-align:center">DATEDIFF()</td>
<td style="text-align:center">日期差值</td>
</tr>
<tr>
<td style="text-align:center">DATE_FORMAT(date,format)</td>
<td style="text-align:center">日期格式化（%Y=年 %m=月 %d=日 %H=时 %i=分 %s=秒）</td>
</tr>
</tbody>
</table>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div></pre></td><td class="code"><pre><div class="line">// 当前时间</div><div class="line">mysql&gt; SELECT NOW();</div><div class="line">+---------------------+</div><div class="line">| NOW()               |</div><div class="line">+---------------------+</div><div class="line">| 2017-07-10 11:16:20 |</div><div class="line">+---------------------+</div><div class="line"></div><div class="line">// 当前日期</div><div class="line">mysql&gt; SELECT CURDATE();</div><div class="line">+------------+</div><div class="line">| CURDATE()  |</div><div class="line">+------------+</div><div class="line">| 2017-07-10 |</div><div class="line">+------------+</div><div class="line"></div><div class="line">// 当前时间</div><div class="line">mysql&gt; SELECT CURTIME();</div><div class="line">+-----------+</div><div class="line">| CURTIME() |</div><div class="line">+-----------+</div><div class="line">| 11:16:38  |</div><div class="line">+-----------+</div><div class="line"></div><div class="line">// 更改时间</div><div class="line">mysql&gt; SELECT DATE_ADD(&quot;2017-07-10&quot;,INTERVAL 1 YEAR);</div><div class="line">+----------------------------------------+</div><div class="line">| DATE_ADD(&quot;2017-07-10&quot;,INTERVAL 1 YEAR) |</div><div class="line">+----------------------------------------+</div><div class="line">| 2018-07-10                             |</div><div class="line">+----------------------------------------+</div><div class="line"></div><div class="line">// 计算时间差</div><div class="line">mysql&gt; SELECT DATEDIFF(&quot;2017-7-10&quot;,&quot;2017-6-10&quot;);</div><div class="line">+-----------------------------------+</div><div class="line">| DATEDIFF(&quot;2017-7-10&quot;,&quot;2017-6-10&quot;) |</div><div class="line">+-----------------------------------+</div><div class="line">|                                30 |</div><div class="line">+-----------------------------------+</div><div class="line"></div><div class="line">// 更改时间格式</div><div class="line">mysql&gt; SELECT DATE_FORMAT(NOW(),&quot;%Y年 %m月%d日%H时%i分%s秒&quot;);</div><div class="line">+------------------------------------------------+</div><div class="line">| DATE_FORMAT(NOW(),&quot;%Y年 %m月%d日%H时%i分%s秒&quot;) |</div><div class="line">+------------------------------------------------+</div><div class="line">| 2017年 07月10日11时28分16秒                    |</div><div class="line">+------------------------------------------------+</div></pre></td></tr></table></figure>
<h1 id="信息函数"><a href="#信息函数" class="headerlink" title="信息函数"></a>信息函数</h1><table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">CONNECTION_ID()</td>
<td style="text-align:center">连接ID</td>
</tr>
<tr>
<td style="text-align:center">DATABASE()</td>
<td style="text-align:center">返回当前数据库</td>
</tr>
<tr>
<td style="text-align:center">LAST_INSERT_ID()</td>
<td style="text-align:center">最后插入记录的数据表的ID字段</td>
</tr>
<tr>
<td style="text-align:center">USER()</td>
<td style="text-align:center">当前用户</td>
</tr>
<tr>
<td style="text-align:center">VERSION()</td>
<td style="text-align:center">当前版本信息</td>
</tr>
</tbody>
</table>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div></pre></td><td class="code"><pre><div class="line">mysql&gt; SELECT CONNECTION_ID();</div><div class="line">+-----------------+</div><div class="line">| CONNECTION_ID() |</div><div class="line">+-----------------+</div><div class="line">|               5 |</div><div class="line">+-----------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT DATABASE();</div><div class="line">+------------+</div><div class="line">| DATABASE() |</div><div class="line">+------------+</div><div class="line">| test       |</div><div class="line">+------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT LAST_INSERT_ID();</div><div class="line">+------------------+</div><div class="line">| LAST_INSERT_ID() |</div><div class="line">+------------------+</div><div class="line">|                5 |</div><div class="line">+------------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT USER();</div><div class="line">+----------------+</div><div class="line">| USER()         |</div><div class="line">+----------------+</div><div class="line">| root@localhost |</div><div class="line">+----------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT VERSION();</div><div class="line">+------------+</div><div class="line">| VERSION()  |</div><div class="line">+------------+</div><div class="line">| 5.7.18-log |</div><div class="line">+------------+</div></pre></td></tr></table></figure>
<h1 id="聚合函数"><a href="#聚合函数" class="headerlink" title="聚合函数"></a>聚合函数</h1><table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">AVG()</td>
<td style="text-align:center">平均值</td>
</tr>
<tr>
<td style="text-align:center">COUNT()</td>
<td style="text-align:center">计数</td>
</tr>
<tr>
<td style="text-align:center">MAX()</td>
<td style="text-align:center">求最大值</td>
</tr>
<tr>
<td style="text-align:center">MIN()</td>
<td style="text-align:center">最小值</td>
</tr>
<tr>
<td style="text-align:center">SUM()</td>
<td style="text-align:center">求总和</td>
</tr>
</tbody>
</table>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div></pre></td><td class="code"><pre><div class="line">mysql&gt; SELECT MAX(goods_price) AS price FROM tdb_goods;</div><div class="line">+-----------+</div><div class="line">| price     |</div><div class="line">+-----------+</div><div class="line">| 28888.000 |</div><div class="line">+-----------+</div><div class="line">1 row in set (0.00 sec)</div><div class="line"></div><div class="line">mysql&gt; SELECT MIN(goods_price) AS price FROM tdb_goods;</div><div class="line">+--------+</div><div class="line">| price  |</div><div class="line">+--------+</div><div class="line">| 99.000 |</div><div class="line">+--------+</div><div class="line">1 row in set (0.00 sec)</div><div class="line"></div><div class="line">mysql&gt; SELECT AVG(goods_price) AS price FROM tdb_goods;</div><div class="line">+--------------+</div><div class="line">| price        |</div><div class="line">+--------------+</div><div class="line">| 5845.1000000 |</div><div class="line">+--------------+</div><div class="line">1 row in set (0.00 sec)</div><div class="line"></div><div class="line">mysql&gt; SELECT SUM(goods_price) AS price FROM tdb_goods;</div><div class="line">+------------+</div><div class="line">| price      |</div><div class="line">+------------+</div><div class="line">| 116902.000 |</div><div class="line">+------------+</div><div class="line">1 row in set (0.00 sec)</div><div class="line"></div><div class="line">mysql&gt; SELECT COUNT(goods_id) AS COUNT FROM tdb_goods;</div><div class="line">+-------+</div><div class="line">| COUNT |</div><div class="line">+-------+</div><div class="line">|    20 |</div><div class="line">+-------+</div><div class="line">1 row in set (0.00 sec)</div></pre></td></tr></table></figure>
<h1 id="加密函数"><a href="#加密函数" class="headerlink" title="加密函数"></a>加密函数</h1><table>
<thead>
<tr>
<th style="text-align:center">函数名</th>
<th style="text-align:center">作用</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:center">MD5()</td>
<td style="text-align:center">信息摘要算法</td>
</tr>
<tr>
<td style="text-align:center">PASSWORD()</td>
<td style="text-align:center">密码算法</td>
</tr>
</tbody>
</table>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div></pre></td><td class="code"><pre><div class="line">mysql&gt; SELECT MD5(&quot;MYSQL &quot;);</div><div class="line">+----------------------------------+</div><div class="line">| MD5(&quot;MYSQL &quot;)                    |</div><div class="line">+----------------------------------+</div><div class="line">| 31d72f67ea8d0f7ee426456e83327af2 |</div><div class="line">+----------------------------------+</div><div class="line"></div><div class="line">mysql&gt; SELECT PASSWORD(&quot;MYSQL &quot;);</div><div class="line">+-------------------------------------------+</div><div class="line">| PASSWORD(&quot;MYSQL &quot;)                        |</div><div class="line">+-------------------------------------------+</div><div class="line">| *50E5F8E9E5335C3578BF217737DB2DCDEDCB8B98 |</div><div class="line">+-------------------------------------------+</div></pre></td></tr></table></figure>

    

    
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